Field of the Invention
This invention relates to the field of stereolithography, which is a technique for making solid, three-dimensional objects (or "parts") from solidifiable fluid or fluid-like materials.
In recent years, stereolithography systems, such as those described in U.S. Pat. No. 4,575,330, issued Mar. 11, 1986 and entitled "Apparatus for Production of Three-Dimensional Objects by Stereolithography," have come into use. Basically, stereolithography is a method for automatically building complex three-dimensional parts by successively solidifying thin cross-sectional layers of photopolymer ("resin") or the like (such as powdered materials, which are converted from a fluid-like medium to a cohesive cross-section by melting and solidification) on top of each other until all of the thin layers are joined together to form a whole part. Photocurable polymers change from liquid to solid in the presence of simulating radiation and their photospeed with ultraviolet light (UV) is fast enough to make them practical model building materials. A radiation source (e.g., an ultraviolet laser) generates a beam which is focused to a small intense spot, which is moved across the liquid photopolymer surface by a galvanometer or servo type mirror x-y scanners. The scanners are driven by computer generated vectors or the like. The material that is not polymerized when a part is made is still usable and remains in the vat as successive parts are made. With this technology, the parts are literally grown from a vat of fluid material (e.g. liquid plastic), and precise complex patterns can be rapidly produced. This method of fabrication is extremely powerful for quickly reducing design ideas to physical form for making prototypes.
This technology typically requires a stereolithography apparatus, referred to as an "SLA," which generally includes a laser scanner, a photopolymer vat, an elevator, and a controlling computer. The SLA is programmed to automatically make a three-dimensional part by drawing it as a sequence of built-up cross-sectional layers.
Stereolithography represents an unprecedented way to quickly make complex or simple parts without tooling. Since this technology depends on using a computer to generate its cross sectional patterns, there is a natural data link to computer aided design and manufacture (CAD/CAM). However, such systems have presented challenges relating to structural stress, shrinkage, curl and other distortions, as well as resolution, speed, accuracy and difficulties in producing certain object shapes.